Conventionally, gas component analysis of flue gas has been generally carried out through wet-format analysis including in situ sampling of analytes from the flue gas or through gas monitoring. In the flue gas analysis, gas components such as nitrogen oxides and sulfur oxides can be sampled in a sampling step without particular technical problems, and can be readily determined at a target accuracy.
The gas components to be determined in the invention, such as ammonia gas, are highly absorbable. These gas components are considerably adsorbed on the inner wall of a flue gas sampling tube during sampling of flue gas. Thus, when a conventional sampling method is employed, a portion of the sampled gas is adsorbed on the inner wall of the tube and remains in the tube, failing to obtain measurements of high accuracy.
In order to solve the above problem, hitherto, such problematic adsorption has been generally mitigated through heating a gas sampling tube. In addition, JIS K0099 stipulates a flue gas ammonia analysis method, in which measures against gas adsorption, such as heating a flue gas introduction tube, are taken. The method stipulated by JIS K0099 is a standard method employed, through manual operations, in an ordinary-scale facility at which flue gas is sampled.
In the case where automatic, continuous gas monitoring is performed in a flue gas sampling site such as a comparatively large-scale flue of a boiler placed in a power plant, the present inventors previously employed a gas sampling method in which a flue gas sampling tube equipped with a large-scale heating mechanism is employed, and a large amount of flue gas is introduced through suction to an auto-analyzer. The method is disclosed in Japanese Patent Nos. 3229088 and 3322420.
However, when the above method is employed, problematic adsorption of gas components occurs due to insufficient heating of a gas sampling tube or an insufficiently heated zone of the tube. Therefore, the method is unsatisfactory when applied to a micro-analysis for determining a concentration of about 100 to about 1 ppm at high accuracy. The adsorption causes loss of the gas component(s) to be analyzed.
Specifically, in the above method, a flue gas is introduced, through suction, into an absorption liquid which absorbs ammonia contained in the flue gas, and the amount of ammonia trapped in the absorption liquid is determined, thereby obtaining the ammonia content of the flue gas. In this step, a portion of ammonia gasp is adsorbed on a surface of the gas sampling tube or other relevant sections. Thus, the adsorbed gas component(s) cannot be trapped in the absorption bottle.
When the above phenomena occur, the obtained analytical values become smaller than expected. Under such circumstances, the present invention is directed to an improvement of the flue gas sampling tube section disclosed in Japanese Patent Nos. 3229088 and 3322420.
Ammonia is a highly water-soluble component and is readily adsorbed on a gas sampling tube. Therefore, upon sampling of ammonia, a sampling tube is generally heated in order to suppress dew formation of water and adsorption of ammonia. In this case, the entirety of the gas sampling tube must be sufficiently heated so as to completely heat insufficiently heated sections. Thus, in order to attain sufficient heating effect particularly in connection portions and a similar portion of the sampling tube, know-how and skills therefor are needed.
The aforementioned conventional methods are unsatisfactory for the micro-component analysis of flue gas. Thus, an object of the present invention is to provide a more reliable gas sampling method, through collecting a gas component deposited on a surface of a flue gas sampling tube, thereby enhancing analysis accuracy.